Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$146.29	6.616%	$155.9685	$155.97	$155.95	$156.00
Purchase #2	$129.51	9.147%	$141.3563	$141.36	$141.35	$141.40
Purchase #3	$37.69	11.367%	$41.9742	$41.97	$41.95	$42.00
Purchase #4	$226.71	7.177%	$242.981	$242.98	$243.00	$243.00
Purchase #5	$60.30	5.473%	$63.6002	$63.60	$63.60	$63.60
Purchase #6	$40.35	8.596%	$43.8185	$43.82	$43.80	$43.80
Purchase #7	$82.53	9.450%	$90.3291	$90.33	$90.35	$90.30
7 purchase totals =	$723.38		$780.0278	$780.03	$780.00	$780.10